Methods and apparatus for inserting multi-lumen split-tip catheters into a blood vessel

ABSTRACT

A method of performing a medical procedure, includes providing a catheter including a first lumen in fluid communication with a first distal opening and a second lumen in fluid communication with a second distal opening, advancing a distal end of a first intra-catheter stiffener element through the first lumen and out of the first distal opening, coupling the first intra-catheter stiffener element to the catheter, advancing a distal end of a second intra-catheter stiffener element through the second lumen and out of the second distal opening, coupling the second intra-catheter stiffener element to the catheter, and advancing the catheter into a patient.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No. 14/094,534, filed Dec. 2, 2013, now U.S. Pat. No. 9,572,956, which is a division of U.S. patent application Ser. No. 13/445,713, filed Apr. 12, 2012, now U.S. Pat. No. 8,597,275, which is a division of U.S. patent application Ser. No. 12/263,141, filed Oct. 31, 2008, now U.S. Pat. No. 8,206,371, which is a continuation of U.S. patent application Ser. No. 10/445,731, filed May 27, 2003, now abandoned, each of which is hereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

The invention relates to methods and apparatus for inserting a catheter into a body cavity and, more particularly, though not exclusively, to methods and apparatus for inserting a multi-lumen split-tip hemodialysis catheter into a blood vessel for hemodialysis.

Multi-lumen catheters are desirable for various treatment applications such as hemodialysis where fluid extraction and infusion occur simultaneously. These multi-lumen catheters provide a single catheter application having multiple lumen channels each supporting independent flow, thus precluding the need for inserting multiple catheters or multiple-catheter assemblies. Further, because a patient might require frequent dialysis, often only days apart, it is desirable to secure placement of the catheter for extended periods of time. Extended placement, however, requires extreme catheter flexibility to avoid damage to the vessel and permit the catheter to move in the blood flow to minimize the possibility of the catheter remaining in pressure contact with the wall of the vessel for prolonged periods.

Unfortunately, the desired flexibility of these catheters presents insertion difficulties. For example, simply advancing the catheter over a guidewire is very difficult since the catheter lacks sufficient stiffness to slide easily through the vessel wall and into the blood vessel to the desired location. Flexible catheters present additional difficulties associated with subcutaneous tunneling and placement.

Known insertion methods and assemblies attempt to overcome, or at least mitigate, these insertion difficulties by stiffening the catheter temporarily during the insertion process. For example, one known method involves temporarily inserting a rigid tubular applicator into one of the lumens. This permits the stiffened catheter/applicator assembly to be passed over a guidewire into a desired position, at which point the applicator can be removed. For example, U.S. Pat. No. 5,405,341 attempts to solve the problem with a single rigid applicator that is designed for insertion into one lumen but also passes through a portion of the second lumen (at the distal end of the instrument) to effectively stiffen the two lumens of the catheter together during insertion. This approach is cumbersome, at best, and presents additional difficulties in maneuvering the instrument. Further, this temporary rigid applicator approach, however, is poorly suited for placement of a catheter having a split at its distal end into two or more separate lumens (e.g., to further isolate a fluid extraction lumen from a return infusion lumen) because only one tip can be secured.

Hence, there exists a need for better and more effective methods and apparatus for insertion of flexible catheters into vessels.

SUMMARY

The invention provides methods and apparatus for inserting flexible, multi-lumen catheters into blood vessels, and in particular, for inserting flexible, split-tip catheters into blood vessels. The invention accomplishes these objects by temporarily stiffening each catheter lumen and tip independently through use of intra-catheter stiffener elements disposed within the catheter lumens. This provides means for advancing the catheter/stiffeners assembly through a subcutaneous tunnel, and over a plurality of guidewires until a distal portion of the catheter is at a desired position within the vessel.

The intra-catheter stiffener elements are sufficiently stiffening to allow advancing the catheter over guidewires, but also sufficiently flexible to allow bending and looping of the catheter for proper placement within the vessel. Further, the intra-catheter stiffener elements prevent catheter kinking during the insertion process. In one embodiment, the intra-catheter stiffener elements have tapered distal ends which can facilitate entry of the catheter/stiffeners assembly into a blood vessel and/or assist in dilating the blood vessel.

One aspect of the invention provides methods and apparatus for inserting an antegrade tunneled, split-tip, hemodialysis catheter into a blood vessel. A distal portion of each of a plurality of guidewires is disposed in a blood vessel at a first location, generally in proximity to the vessel in which a portion of the catheter is to be placed. A subcutaneous tunnel is formed between the first location and a second location where a proximal end of the catheter can extend from the patient. An intra-catheter stiffener element is inserted into the proximal end of each catheter lumen until it extends beyond the distal end of that catheter lumen. The intra-catheter stiffener element can be releasably coupled, following insertion, to the proximal end of its respective catheter lumen via, for example, a mating luer assembly. Each guidewire can be inserted into to a distal end of a lumen in a respective intra-catheter stiffener element until that guidewire extends from the proximal end of that intra-catheter stiffener element. The catheter can then be advanced over the guidewires and into the blood vessel. Alternatively, the catheter can be advanced over the guidewires until a distal end of the catheter is adjacent to the vessel, at which point the catheter and guidewires can be advanced together into the vessel until the distal end of the catheter is at a desired location therein. Twisting the catheter while simultaneously advancing it along the guidewires can facilitate placement of the catheter into the vessel.

In another aspect, the methods and apparatus of the invention provide for inserting a retrograde tunneled hemodialysis catheter into a blood vessel. A distal portion of each of a plurality of guidewires is inserted into a blood vessel at a first location generally as described above. An intra-catheter stiffener element is placed in each catheter lumen until it extends from a distal end of the catheter, and can be releasably connected to the proximal end of its respective catheter lumen, as noted above. A proximal end of each guidewire is threaded through the distal end of a lumen of each intra-catheter stiffener element until the guidewire extends beyond the proximal end of that stiffener element. The catheter is advanced over the guidewires, optionally using a twisting motion, until a distal portion of the catheter is disposed at a desired location within the vessel, or alternatively, the catheter can be advanced until its distal end is adjacent to the vessel, at which point the catheter and guidewires can be advanced together until the distal end of the catheter is disposed at a desired location within the vessel. The guidewires are removed from the catheter lumens. A subcutaneous tunnel is then formed between the first location and a second location, and the proximal end of the catheter is passed through the first location until it extends from the second location. (If the stiffener elements have not previously been removed, they can be removed from the catheter body following passage of the catheter through the tunnel.) An access port is connected to the proximal end of each of the catheter lumens allowing fluid connection with a treatment device, such as a hemodialysis infuser.

In a related aspect, the methods and kits of the present invention can provide for dilating the desired vessel subsequent to inserting the distal portion of a first guidewire. For example, a size 6-French sheath/dilator can be threaded over the first guidewire. Further guidewires can then be inserted into the expanded vessel, or through a lumen in the sheath and into the vessel. After placement of the guidewires into the vessel, the dilator or sheath can be removed.

In a further related aspect, the methods provide for tunneling between the first and second location by using a pointed stylet. A distal end of a pointed stylet can be inserted through the skin at the second location and pushed toward the first location until the distal end extends therefrom. The distal end of the catheter is removably attached to a proximal end of the stylet. The stylet is then pulled from the first location until the distal end of the catheter extends therefrom, to facilitate an antegrade tunneled catheter.

Alternatively, a pointed distal end of a stylet can be inserted through the skin at the first location and pushed until it extends from the second location. The proximal end of the catheter can be removably attached to the proximal end of the stylet. The stylet is then pulled back toward the second location until the proximal end of the catheter extends therefrom. The catheter is then released from the stylet, thus positioning a retrograde tunneled catheter. To facilitate movement of the catheter within the tunnel, the proximal end of the catheter having mating lures or other coupling features can be removed or severed prior to attachment to the stylet. After tunneling the catheter, fluid couplings or other attachments can be disposed to the proximal end of the lumens.

Preferably, the vessel is expanded to accommodate placement of the distal portion of the catheter in the vessel. Vessel dilators of increasing size can be sequentially inserted into the vessel for this purpose. For example, a size 12-French dilator followed by a size 14-French, which is then followed by a size 16-French dilator, can be inserted into the vessel before advancing the catheter along the guidewires. In other embodiments, fewer (or more) dilators of different sizes can be used. Differing size and number of vessel dilators can be used corresponding to the catheter chosen for the desired application. Use of intra-catheter stiffener elements can preclude use of vessel dilators sized larger that the catheter since the stiffener elements and the catheter itself can provide vessel dilation.

Another aspect of the invention provides for apparatus, in the form of a kit, to insert a multi-lumen catheter into a blood vessel. The kit comprises guidewires each adapted to have a distal portion inserted into a blood vessel. A plurality of intra-catheter stiffener elements preferably having tapered distal ends are also provided, each having a lumen extending along its length sized to accommodate a guidewire, and each having an outside diameter sized to be slidably disposed within a lumen of the catheter. The intra-catheter stiffener elements can be provided in one or more predetermined lengths corresponding to a length of a catheter and its lumens selected for a particular use, or can be of the same length. Further, the intra-catheter stiffeners can be provided with mating devices, such as lures, disposed at a proximal end correspond with mating connectors disposed at a proximal end of the catheter lumens.

One or more vessel dilators can also be provided in the kit, each corresponding in size to a particular application. For example, a size 6-French sheath/dilator can be provided to dilate the vessel to accommodate a plurality of guidewires. A size 12-French, 14-French, as well as a size 16-French, dilator can be provided to dilate the vessel to accommodate the distal tip of the catheter.

The present invention is applicable in the field of hemodialysis, among others, for inserting a multi-tip catheter into a blood vessel. The methods and apparatus provide for insertion of a split-tip catheter without using a tearable sheath and avoid the problems associated with prior art approaches of split tip catheter insertion over a single guidewire.

BRIEF DESCRIPTION OF THE INVENTION

These and other objects, advantages and features of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a schematic, partially cutaway, side view of a hemodialysis catheter insertion system according to the invention;

FIG. 2 is a schematic illustration of an initial step of a method according to the invention in which a distal portion of a first guidewire is inserted in a vessel;

FIG. 3 is a schematic illustration of another step of the method of the invention in which a blood vessel dilating sheath and a distal portion of a second guidewire are inserted in a vessel;

FIG. 4 is a schematic illustration of another step of the method in which an antegrade catheter is disposed in a subcutaneous tunnel between a first location and a second location according to the invention;

FIG. 5 is a schematic illustration of another step of the method in which the first guidewire is threaded through a first lumen of a catheter assembly according to the invention, in which the catheter assembly has an intra-catheter stiffener element disposed in each lumen of the catheter;

FIG. 6 is a schematic illustration of another step of the method in which the second guidewire is threaded through the second lumen of the catheter assembly to a point where two loops of guidewire remain to facilitate placement of the distal end of the catheter in the vessel;

FIG. 7 is a schematic illustration of another step of the method in which the catheter assembly has been advanced along the guidewires until the distal portion of the catheter is positioned within the vessel at a desired location;

FIG. 8 shows the catheter of FIG. 7 with the intra-catheter stiffener elements and guidewires removed;

FIG. 9 is a schematic illustration showing a step of a method according to the invention wherein a retrograde catheter is shown having a distal end disposed in a vessel;

FIG. 10 is a schematic illustration showing a further step of the method wherein the catheter has been subcutaneously tunneled subsequent;

FIG. 11 shows the catheter with fluid-couplers installed; and

FIG. 12 shows a kit according to the invention for installing catheters such as those described above.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a catheter system 10 according to the invention is shown having a catheter body 12 with two internal lumens 14A and 14B. The catheter body 12 has a “split-tip” distal end 16 in which the body (and lumens) separate into two distal tip portions, 18A and 18B, which form a single-lumen distal blood removal extension tube and a single-lumen distal blood return extension tube, respectively. The split tips can, but need not have one or more side ports 20A and 20B, in fluid communication with one or the other of the lumens to facilitate blood removal and return, respectively, during hemodialysis. Alternatively, or in conjunction with side ports, the distal ends can be open to provide fluid passageways for blood removal and return. The proximal end 22 of the catheter body can also be split into separate segments 22A and 22B and terminates with two access ports 28A and 28B, which can include couplings 34A and 34B, such luer-locks or the like, to couple the catheter to a hemodialysis machine in which blood is circulated and purified. Proximal segments 22 A and 22 B thus provide a single-lumen proximal blood removal extension tube and a single-lumen proximal blood return extension tube, respectively. The overall system or kit of the invention can also include two intra-catheter stiffener elements 24A and 24B and two guidewires 26A and 26B (shown within the respective lumens 14A and 14B). The catheter body 12 is typically a very flexible silicone, polyurethane or other biocompatible composition (e.g., having a stiffness in the range of about 65 to about 85 durometers). Preferably, the intra-catheter stiffener elements 24A and 24B are composed of a stiffer form of polyethylene or other bio-compatible material. In addition to stiffening the assembly, the stiffener elements can also help to prevent kinking of the catheter during insertion.

The catheter system 10 of FIG. 1 provides for insertion of the distal end of the multi-lumen, split-tip, flexible catheter body 12 into a blood vessel using the intra-catheter stiffener elements and guidewires, as will be explained below. Briefly, a distal portion of each guidewire is disposed at a desired position within the vessel. An intra-catheter stiffener element having a tapered tip to facilitate insertion into the vessel and to provide catheter stiffening is slidably disposed along the length of each catheter lumen until it extends beyond the distal tip of that catheter lumen. A proximal end of each guidewire is threaded through a distal end of a lumen extending along each of the intra-catheter stiffener elements. The catheter is then advanced over the guidewires and into the blood vessel. Alternatively, the catheter can be advanced over the guidewires until the distal end is adjacent to the vessel, at which point the catheter and guidewires can be advanced together into the blood vessel. The guidewires and intra-catheter stiffener elements are then removed from the catheter. The methods and application kit described can be used for any split-tip catheter, and are particularly useful for insertion of subcutaneously tunneled hemodialysis catheters.

A method of insertion according to the invention will next be described in connection with FIGS. 2-8. The procedure involves not only inserting the catheter tips into a blood vessel but also forming a subcutaneous tunnel below a patient's skin to secure the catheter in place and is sometimes described as antegrade or forward insertion. It will be appreciated, however, that the methods described herein can be used for inserting catheter tips into a blood vessel where tunneling is not necessary or desired.

FIG. 2 schematically shows an initial step of a method according to the invention in which a distal portion of a first guidewire 26A is inserted in a vessel 4 of a patient 2. The entry location 6 of the guidewire 26A is referred to herein as the “first location” or the “venotomy site.” This first location is typically a surgical incision that provides access to the desired blood vessel which typically includes the internal or external jugular, femoral or subclavian vein, and the vena cava, for example. In one preferred embodiment, the blood vessel chosen for catheter placement can be the right side internal jugular vein.

In FIG. 3, a blood vessel sheath/dilator 30 is shown inserted over the first guidewire 26A to dilate the vessel. The distal portion of a second guidewire 26B is then inserted in the vessel 4 via the sheath/dilator 30.

With reference to FIG. 4, a subcutaneous tunnel 40 is formed (before or after the insertion of guidewires 26A and 26B) to anchor the catheter body in place and provide two remote ports for coupling the two lumens of the catheter to a dialysis machine. In FIG. 4, a catheter body 12 of an antegrade catheter has been disposed in a subcutaneous tunnel 40 between the first (venous access) location 6 and a second (exit) location 32, such that the distal end of the instrument including the split tips 18A and 18B extend from the first location. Prior to insertion, each of the lumens of catheter body 12 has been fitted with a hollow, tubular, intra-catheter stiffener element or liner, 24A and 24B, respectively.

In FIG. 5, the first guidewire 26A is threaded through a first lumen of the catheter assembly (i.e., through the lumen of intra-catheter stiffener element 24A). In FIG. 6, the second guidewire 26B is threaded through the second lumen of the catheter assembly (i.e., through the lumen of intra-catheter stiffener element 24B). Each of the guidewires is advanced through the catheter assembly to a point where two short loops of guidewire remain to facilitate placement in the vessel.

As shown in FIG. 7, the catheter assembly is then advanced along the guidewires until the distal end 16 of the catheter is positioned at a desired position within the vessel. In a preferred embodiment, the catheter is advanced over the guidewires until the distal end is adjacent to the vessel, and then the catheter and the guidewires can be advanced together until the distal end of the catheter is positioned at a desired position within the vessel. The guidewires 26A and 26B can then be removed by withdrawing them via the proximal end 22 of the catheter body. Likewise, the intra-catheter stiffener elements 24A and 24B can be removed (either subsequent to the guidewires or at the same time).

Advantageously, this method precludes using a vessel dilator larger than the catheter/stiffeners assembly for placement of the catheter within the vessel since the intra-catheter stiffener elements and the catheter itself provide vessel dilation.

FIG. 8 shows the catheter of FIG. 7 with the intra-catheter stiffener elements and guidewires removed. The venous access incision is then closed and the catheter is secured subcutaneously (e.g., via an implanted cuff and/or sutures).

Although the above detailed description has been presented in connection with an antegrade insertion, it should be clear that the methods and systems of the present invention are equally useful in retrograde or reverse insertions (where the catheter body is passed through the subcutaneous tunnel from venotomy site to the remote exit location).

Thus, a method according to the invention for insertion of a retrograde catheter will next be described. An initial step for insertion of a retrograde catheter begins with placement of guidewires within the vessel as described above in connection with FIGS. 2 and 3.

FIG. 9 illustrates a step of the method wherein the catheter body 12 has each of the lumens fitted with a hollow, tubular, intra-catheter stiffener element or liner, 24A and 24B, respectively. The intra-catheter stiffener elements can have a coupler at a proximal end that releasably couple to a mating coupler at a proximal end of the respective catheter lumen. Guidewires 26A and 26B are threaded through the lumens of the catheter assembly as described above in FIGS. 5 and 6. The catheter body is advanced along the guidewires until the distal end of the catheter in a desired location within the vessel. Alternatively, the catheter body can be advanced along the guidewires until the distal end is adjacent to the vessel, and then the catheter and the guidewires can be advanced until the distal end is located at a desired position within the vessel. The guidewires and, optionally, the intra-catheter stiffener elements are then removed from the lumens.

FIG. 10 shows a step of the method wherein the catheter has been subcutaneously tunneled. A subcutaneous tunnel is formed between a second location 32 (exit location) and the first location 6 (venotomy site). Tunneling between the first and second location by using a pointed stylet or trocar 94. Couplers at the proximal end 22 of the catheter lumens are removed, or alternatively, severed therefrom to allow the proximal end of the catheter to be pulled through the tunnel 40. In one embodiment, the proximal end of the catheter is pulled through subcutaneous tunnel from the first location until it extends from the second location. In this embodiment, a pointed distal end of a stylet 94 can be inserted through the skin at the first location and pushed until it extends from the second location. The proximal end of the catheter can be removably attached to the proximal end of the stylet using connector 96. The stylet is then pulled back toward the second location until the proximal end of the catheter extends therefrom.

FIG. 11 illustrates the catheter after tunneling with access ports 28A and 28B installed, or alternatively, replaced and coupled to a hemodialysis machine 80 through legs 82, 84 for blood purification.

As noted above, it will be appreciated that the use of the intra-catheter stiffener elements provide sufficient stiffness so that the flexible split tips can be slid over the guidewires into the desired position with less effort and reduced likelihood of trauma. Catheter kinking is mitigated during the insertion process, thus reducing complexity of catheter insertion.

FIG. 12 shows contents of a preferred embodiment of a kit 48 providing equipment to perform the above described methods. Illustrated are two intra-catheter stiffener elements 50A and 50B, two guidewires 52A and 52B, a 6-French sheath/dilator 54 and two vessel dilators of differing sizes 56 and 58. It will be appreciated by one skilled in the art that other arrangements are contemplated, each having at least two intra-catheter stiffener elements. For example, in one embodiment, the insertion kit has a split-tip catheter and two intra-catheter stiffener elements. The kit is suitable for insertion of either antegrade or retrograde catheter configurations according to the illustrated methods described above.

Intra-catheter stiffener elements 50A and 50B are illustrated as 5-French in size and of the same length. However, intra-catheter stiffener elements 50 need not be of the same size and length, but can be selected according to the size and length of the catheter to be inserted. Further, intra-catheter stiffener elements need not have a round exterior shape, but rather, can have an external shape according to the size and shape of an interior of a catheter lumen, for example, oval shaped. In a preferred embodiment, each intra-catheter stiffener element has a tapered configuration along a distal portion to aid in dilating the catheter lumen, with a releasable coupler at a proximal end such as a luer-coupler at a proximal end. Each has a hollow bore or lumen running along its length sized to slidably receive a guidewire as described above. Each preferably has stiffness sufficient to prevent the catheter from kinking or otherwise distorting during the insertion procedure. It will be appreciated that the intra-catheter stiffener elements can be in kit form as separate from, or disposed within, the catheter lumens.

Guidewires 52A and 52B are illustrated as J-straight 0.038″ guidewires, however each can vary according to the application and catheter configuration. Each can have a removable sheath to accommodate handling and facilitate placement within a desired location such as a vein.

Sheath/dilator 54 is illustrated as size 6-French, however, other sizes may be used to puncture a wall of a vessel and accommodate one or more guidewires. Dilators 56 and 58 are illustrated as size 14-French and 16-French, respectively, and are suitable for many catheter insertion procedures. In a preferred embodiment, a size 12-French is provided in addition to or instead of one of the illustrated dilators.

It will be appreciated, therefore, that the above methods and kits are useful for inserting hemodialysis catheters in a patient, and in general for multi-lumen split-tip catheters intended for other functions where body fluids are extracted and introduced. As such, the invention is not limited to those embodiments described above, but rather, is limited by the claims that follow. 

What is claimed is:
 1. A method of performing a medical procedure, comprising: providing a catheter including a first lumen in fluid communication with a first distal opening and a second lumen in fluid communication with a second distal opening; advancing a distal end of a first intra-catheter stiffener element through the first lumen and out of the first distal opening, the first intra-catheter stiffener element including a first guidewire lumen; coupling the first intra-catheter stiffener element to the catheter; advancing a distal end of a second intra-catheter stiffener element through the second lumen and out of the second distal opening, the second intra-catheter stiffener element including a second guidewire lumen; coupling the second intra-catheter stiffener element to the catheter; advancing the catheter into a patient; uncoupling the first intra-catheter stiffener element from the catheter and removing the first intra-catheter stiffener element from the first lumen; and uncoupling the second intra-catheter stiffener element from the catheter and removing the second intra-catheter stiffener element from the second lumen.
 2. The method according to claim 1, wherein the advancing the catheter comprises: positioning a distal end of a guidewire at a desired position in the patient; threading a proximal section of the guidewire through the second guidewire lumen; and advancing the catheter over the guidewire into the patient.
 3. The method according to claim 2, further comprising removing the guidewire from the second guidewire lumen prior to uncoupling the first and second intra-catheter stiffener elements from the catheter.
 4. The method according to claim 1, further comprising forming a subcutaneous tunnel between a first location and a second location.
 5. The method according to claim 4, further comprising: removably attaching a distal end of the catheter to a tunneling member; moving the tunneling member and the catheter through the subcutaneous tunnel until the catheter distal end exits the tunnel; and removing the catheter from the tunneling member.
 6. The method according to claim 1, wherein following the advancing the distal ends of the first and second intra-catheter stiffener elements out of the first and second distal openings and coupling the first and second intra-catheter stiffener elements to the catheter, the distal end of the first intra-catheter stiffener element is distal of the distal end of the second intra-catheter stiffener element.
 7. The method according to claim 1, wherein the distal ends of the first and second intra-catheter stiffener elements are tapered to facilitate the advancing the catheter into the blood vessel.
 8. The method according to claim 1, wherein the coupling the first intra-catheter stiffener element to the catheter comprises coupling a first coupler at a proximal end of the first intra-catheter stiffener element to a first mating coupler at a first proximal opening of the catheter.
 9. The method according to claim 8, wherein the coupling the second intra-catheter stiffener element to the catheter comprises coupling a second coupler at a proximal end of the second intra-catheter stiffener element to a second mating coupler at a second proximal opening of the catheter.
 10. The method according to claim 1, wherein the first intra-catheter stiffener element has a first length and the second intra-catheter stiffener element has a second length less than the first length.
 11. The method according to claim 1, wherein the first intra-catheter stiffener element has an exterior shape that matches the cross-sectional shape of the first lumen and the second intra-catheter stiffener element has an exterior shape that matches the cross-sectional shape of the second lumen.
 12. The method according to claim 11, wherein the exterior shape of the first intra-catheter stiffener element is round or oval.
 13. The method according to claim 11, wherein the exterior shape of the second intra-catheter stiffener element is round or oval. 